U.S. patent application number 12/670921 was filed with the patent office on 2011-01-20 for nanoporous silicate membranes for portable fuel.
This patent application is currently assigned to UNIVERSITY OF WYOMING. Invention is credited to Debashis Dutta.
Application Number | 20110014546 12/670921 |
Document ID | / |
Family ID | 40304788 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110014546 |
Kind Code |
A1 |
Dutta; Debashis |
January 20, 2011 |
Nanoporous Silicate Membranes for Portable Fuel
Abstract
A fuel cell is disclosed which has a significantly reduced
internal resistance and which can be miniaturized. Two substrates
are prepared, on with microchannels running along its facing
surface and the other with nanochannels running along its facing
surface. A silica-based binder is used to bind the substrates
together with the microchannels running orthogonal to the
nanochannels. The binder is removed from the microchannels and a
fuel is introduced into at least one of the microchannels and an
oxidant is introduced into at least one other of the
microchannels.
Inventors: |
Dutta; Debashis; (Laramie,
WY) |
Correspondence
Address: |
DAVIS, BROWN, KOEHN, SHORS & ROBERTS, P.C.;THE DAVIS BROWN TOWER
215 10TH STREET SUITE 1300
DES MOINES
IA
50309
US
|
Assignee: |
UNIVERSITY OF WYOMING
Laramie
WY
|
Family ID: |
40304788 |
Appl. No.: |
12/670921 |
Filed: |
July 28, 2008 |
PCT Filed: |
July 28, 2008 |
PCT NO: |
PCT/US08/71352 |
371 Date: |
September 9, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60962273 |
Jul 27, 2007 |
|
|
|
Current U.S.
Class: |
429/512 |
Current CPC
Class: |
H01M 8/0245 20130101;
H01M 8/0236 20130101; H01M 4/861 20130101; Y02E 60/50 20130101;
H01M 8/1004 20130101; H01M 4/8605 20130101; H01M 4/8657
20130101 |
Class at
Publication: |
429/512 |
International
Class: |
H01M 8/04 20060101
H01M008/04 |
Claims
1. A fuel cell, comprising: (a) a first substrate having at least a
pair of microchannels extending along a facing surface thereof; (b)
a second substrate having a plurality of nanochannels extending
along a facing surface thereof; (c) a silica-based binder applied
to at least one of the facing surfaces; (d) the substrates being in
contact with each other with the binder between the adjoining
facing surfaces with the microchannels transverse to the
nanochannels; (e) wherein the binder is removed from the
microchannels; and (f) a fuel present in at least one of the
microchannels and an oxidant present in at least one of the other
microchannels.
2. The fuel cell of claim 1, wherein the first and second
substrates are glass.
3. The fuel cell of claim 1, wherein the silica-based binder is
sodium silicate.
4. The fuel cell of claim 1, wherein the microchannels are between
about 10 and about 100 microns deep and between about 200 and about
1000 microns wide.
5. The fuel cell of claim 1, wherein the nanochannels are between
about 50 and about 500 nanometers deep and about 100 and about 500
microns wide.
Description
[0001] This application claims priority to U.S. Patent Application
Ser. No. 60/962,273, filed Jul. 27, 2007, and incorporated herein
by this reference.
BACKGROUND OF THE INVENTION
[0002] The invention relates generally to fuel cells and, more
specifically, to fuel cells having nano-scale porous silicate
membranes.
[0003] A fuel cell is an electrochemical energy conversion device.
It produces electricity from external supplies of fuel (on the
anode side) and oxidant on the cathode side, which react in the
presence of an electrolyte. Fuel cells differ from batteries in
that they consume reactants, which must be replenished, while
batteries store electrical energy chemically in closed system.
Additionally, while the electrodes within a battery react and
change as a battery is charged or discharged, the electrodes in a
fuel cell are catalytic and relatively stable. Fuel cells are
usually compact, lightweight with no moving parts and are very
useful as power sources in remote locations. Because fuel cells
have no moving parts, and do not involve combustion, they can
achieve very high reliability or in other words they have very
little down time over their life period. Fuel cells also tend to
have much higher efficiencies in converting chemical energy to
electrical energy especially when operated under low power density
conditions.
[0004] The current state-of-art for commercial portable fuel cells
consists of primarily two designs. The first among these involve a
cathodic and an anodic compartment clamped to each other with a PEM
(typically Nafion) sandwiched between them. Such architectures
usually have a high electrical resistance dominated by that of the
nanoporous Nafion membrane which is typically about 200 microns
thick. The other commercial design for portable fuel cell does not
require any membrane between the cathodic and the anodic
compartment but rely on continuous laminar flow of fluid within it
at high speeds (.about.1 cm/s) to prevent the fuel and oxidant
streams from mixing. Although this design has a much lower
electrical resistance, it requires continuous pumping of the fluid
via external means. Also, the continuous flow of the oxidant and
the fuel in the device allows only about 30% usage of the chemicals
yielding low efficiencies.
SUMMARY OF THE INVENTION
[0005] The invention consists of microfluidic fuel cells that
include silca based nanoporous/sol-gel structures used as an
ion-selective membrane for a polymer electrolyte membrane. Two
microchannels are created on a first or bottom glass substrate. A
plurality of nanochannels are created on a second or top glass
substrate. The microchannels of the substrates are oriented
orthogonally relative to the nanochannels and sealed by bonding the
two substrates together with a suitable bonding agent, such as
sodium silicate. Excess bonding agents is pumped out of the
microchannels but remains in the nanochannels where it is
transformed into silica gel during curing. A fuel cell fuel fills
one of the microchannels and a fuel cell oxidant fills the other of
the microchannels.
[0006] An object of the present invention is to provide a fuel cell
have a low internal resistance.
[0007] Another object of the invention is to provide a miniaturized
fuel cell that resists leakage of fuel or oxidant.
[0008] A further object of the invention is to provide a fuel cell
that does not require flowing fuel or oxidant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a chart of the performance of a microfluidic fuel
cell of the present invention carrying 1M methanol in 0.5M sulfuric
acid as the fuel and 0.15M potassium permanganate in 0.5M sulfuric
acid as the oxidant at 50.degree. C.; platinum electrodes were
employed in both the cathodic and the anodic compartments in these
experiments to carry out the electrochemical reactions.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0010] This invention disclosure describes the fabrication of
silica based nanoporous/sol-gel structures that can be used as an
ion-selective membrane or support for a polymer electrolyte
membrane (PEM) e.g., Nafion, in portable microfluidic fuel cells. A
unit of such a fuel cell comprises of two microchannels that are
between about 10 and about 100 microns deep and between about 200
and about 1000 microns wide, created on a glass substrate,
preferably using standard photolithographic and wet etching
techniques. To seal off these channels a second glass plate is
bonded to this substrate using a thin layer of sodium silicate
solution, preferably about 5% by weight, as a binder. A series of
nanometer scale channels between about 50 and 500 nanometers deep
and about 100 and about 500 microns wide, are created on this cover
plate prior to the bonding process, preferably by chemical etching.
The two plates are brought in contact during the bonding process in
such a way that the nanochannels run transverse, and preferably
orthogonal, to the microchannels in the bottom substrate. Once the
cover plate and the base substrate have been put together excess
sodium silicate entering the microchannels are pumped out using a
vacuum supply. The solution within the nanometer scale channels
however, does not escape due to the large capillary forces. The
device is then treated at 90-120.degree. C. in a conventional over
under ambient pressure for about 15-30 minutes. During the heating
process the sodium silicate solution in the nanochannels turns into
silica gel, a porous hard glassy substance. The bonding between the
two plates is finally allowed to complete under ambient conditions
for about 12 hours. The device is then operated by filling up one
of the microchannels with a fuel e.g., 1M methanol in 0.5M sulfuric
acid, and other one with an oxidant e.g., 0.15M potassium
permanganate in 0.5M sulfuric acid. Upon bringing in contact two
platinum electrodes to these fluid streams in the microchannels, a
voltage can be generated in the system.
[0011] In this circuitry, the porous silicate structure acts as an
ion-selective membrane that preferentially allows only
cationic/anionic species to pass through it depending on the
operating conditions. Scientific literature suggests that this
ion-selectivity of silica-based sol-gel structures may be due to
the inherent negative charges on their surfaces which tends
electrostatically attract only the cationic species towards them.
Depending on the solution pH this ion-selectively can be tuned to
selectively allow cations or anions to pass through them. In other
instances, the sodium silicate derived sol-gel structure can used
as a support for a polymer electrolyte membrane that again only
allows certain ions to pass through them. In our current work, this
has been demonstrated by coating the sot-gel structure with a
Nafion solution available commercially. Our data shows the latter
design to be more effective due to its lower resistance to
ion-conduction yielding in larger currents for a given fuel cell
architecture (FIG. 1).
[0012] The present invention offers several advantages over the two
prior art devices described above. Because the thickness of the
nanoporous membrane in the current design can be fabricated down to
a size of about 10 micrometers, the internal electrical resistance
of the fuel cell is significantly reduced (.about.10 .OMEGA.).
Further, the incorporation of the membrane within the fuel cell
allows significant miniaturization of the device and prevents any
issues with leakage of the chemicals from the system. Moreover, no
flow of the oxidant/fuel is required in this device as the sodium
silicate derived membrane prevents their mixing in the system. It
is important to note that the current architecture may also allow
the integration of multiple fuel cells (scale-up) on a single
footprint yielding voltages 1-2 orders of magnitude higher than
those could be generated using a single fuel cell. Moreover,
because the current device is made from glass-based substrate its
optical transparency (compared silicon based devices) can allow the
realization solar fuel cells. In these designs, instead of
supplying a fuel stream to the microchannels certain
proteins/bio-organisms that can utilize solar energy to generate
fuels will be placed in the conduits. Also, the requirement of an
oxidant stream in these units may be eliminated by bringing in
contact the silicate derived membranes to a solution rich in
molecular oxygen.
[0013] The present invention can have a large impact particularly
in running low power devices in remote locations, such as
spacecraft, remote weather stations, large parks, rural locations
and in certain military applications. It is expected that the
simpler fabrication procedure and the requirement of no flow in
these devices can significantly reduce the cost involved in
producing portable fuel cells and also allow their usage over a
wider range of applications, for example, through use of
proteins/bio-organisms that can produce fuel using solar energy.
Moreover, realization of larger power outputs from these devices
through integration of multiple fuel cells in series on a single
footprint may allow the realization of high energy portable power
sources for the future.
[0014] The foregoing description and drawings comprise illustrative
embodiments of the present inventions. The foregoing embodiments
and the methods described herein may vary based on the ability,
experience, and preference of those skilled in the art. Merely
listing the steps of the method in a certain order does not
constitute any limitation on the order of the steps of the method.
The foregoing description and drawings merely explain and
illustrate the invention, and the invention is not limited thereto,
except insofar as the claims are so limited. Those skilled in the
art that have the disclosure before them will be able to make
modifications and variations therein without departing from the
scope of the invention.
* * * * *